Liquid crystals, highly anisotropic fluids intermediate in character between solids and more conventional isotropic liquids, are possessed of constituent molecules exhibiting some degree of order despite being in a non-solid state within certain ranges of temperature. Liquid crystals are typically organic compounds. Where ordered, an illusion of solid like property is imparted to the liquid crystal, but forces of traction between constituent molecules typically are not sufficiently strong to prevent some flow or other substantial property atypically associated with a solid. Thousands of organic substances and particularly, many polymers exhibit liquid crystallinity.
Typically, a liquid crystal exhibits a solid phase which, at a particular temperature, changes by melting to yield a fluid in which, to some degree, the original molecular order of the solid is retained. Upon a further temperature elevation, a second melting point is reached at which the liquid crystal assumes a more normal or typical isotropic liquid phase. Significant alignment properties between the constituent molecules is generally eliminated by such a second melting. For some liquid crystals, solid-state-resembling intermolecular order may also be at least partially destroyed by the introduction of a solvent into the liquid crystal. Such solvent destroyed liquid crystals are termed lyotropic.
Liquid crystals can demonstrate a variety of phases. Two more common phases are the so-called smectic and nematic. In both phases, molecules of the liquid crystal material tend to demonstrate parallel orientation along long axes of the liquid crystal molecules. Additionally, many smectic liquid crystal forms demonstrate a layering of molecular centers into two dimensional planes or sheets. Because a smectic mesophase tends to be the most solid-like of liquid crystal phase structures, it is more common for processing of liquid crystals to be undertaken in the nematic phase. In many liquid crystals, both smectic and nematic phase behavior are observed with the less ordered nematic phase behavior as a rule occurring at a more elevated temperature than that characterizing the smectic phase behavior in the particular liquid crystal.
Liquid crystals, however, like most materials, pass from a more ordered state to a less ordered state with increasing temperature. So, liquid crystalline materials pass from a solid state to, in many instances, a smectic liquid crystal state and then to a nematic liquid crystal state with increasing temperature. From time to time, depending upon the nature of the liquid crystal material, a mesophase state may be achieved only where the temperature of the particular liquid crystalline material approaches or exceeds a temperature at which the liquid crystalline material begins to decompose.
Where a liquid crystalline material is possessed of a mesophase state over a temperature range that approaches or exceeds the decomposition temperature for the liquid crystalline material, processing of the liquid crystalline material in the mesophase state can become difficult if not impossible. Particularly, nematic state processing may be desirable because of the lower degree of order associated with material in a nematic phase versus a smectic phase liquid crystalline material.
Yet, the introduction of a mere solvent into a liquid crystal material to assist in lowering the degree of order of the liquid crystal material likely and thereby lowering the temperature at which the liquid crystalline material would be processable, may result in the conversion of the liquid crystal material into a lytropic state unsuitable for melt processing. Alternately, introduction of the solvent could destroy liquid crystallinity entirely. In any event where a solvent is included as a processing assistor, any such solvent must, typically, later be removed. Techniques for such removal can interfere with ultimate uses for the liquid crystal material being processed.
In other liquid crystal materials, the temperature range in which the liquid crystal material forms a mesophase may be sufficiently below a degradation temperature for melt processing of the liquid crystal material, but a viscosity associated with the liquid crystal material in the temperature range associated with mesophase behavior may be sufficiently elevated to preclude, effectively, the application of desirable melt processing techniques. For reasons similar to those applicable to a situation where the mesophase behavior occurs in a temperature range insufficiently distinct from the degradation temperature, the addition of a solvent to alter mesophase viscosity characteristics may often be undesirable. A liquid crystalline material having an elevated viscosity while in the mesophase at a desirable processing temperature or a liquid crystal material having a temperature range in which mesophase behavior is demonstrated closely adjacent or above a temperature at which degradation of the liquid crystal material occurs often is found in polymeric liquid crystalline materials and particularly synthetic polymeric liquid crystals.
A method for processing a liquid crystal material having elevated viscosity within a temperature processing range or a temperature range in which the liquid crystal material is processible only so closely adjacent or exceeding a decomposition temperature for the liquid crystal material as to make processing within that temperature range impractical but without necessitating subsequent removal of a solvent from the liquid crystal material being processed could find widespread commercial utility.